It's undoubtedly good new for our planet's ailing marine life, but there's one statistic both supermarkets are not telling you about and it's deeply concerning for environmentalists.

Both supermarkets continue to offer customers thicker reusable bags at 15 cents a pop and they're not saying how many of these they've sold since ditching single-use bags earlier this year.

The director of environmental group Boomerang Alliance's, Jeff Angel, said that supermarkets still had much more to do to wipe out plastic usage completely.

"We said to the supermarkets good on you for ending the flimsy give away bags but don't replace them with the plastic bags that cost 15 cents. That is what is happening and still ending up in landfill and the environment," he told Today this morning.

"It is good that we have made that first step and 80 per cent of the free flimsy lightweight bags are gone from the checkout.

"We really have to reduce single use plastics. These bags aren't reuseable. They might be used once or a couple of times then they are ending up in landfill.

"What we want the supermarkets to focus on are the thicker bags, clothe, other types of material that you can use hundreds and hundreds of times.

"That's what is good for the environment not producing billions. This is an accurate figure. Billions more of these replaceable bags and dumping them in landfill."

However, Woolworths said shoppers had embraced the switch to using reusable bags or buying thicker canvas bags for $1 each.

And, Coles responded by saying it will continue to offer reusable plastic bags "to customers who forget to bring their bags from home".

Both supermarkets' decision to stop offering single-use disposable plastic bags midway through the year was initially met with swift public backlash. But three months on the radical change has translated to an 80 per cent drop in the consumption of plastic bags nationwide, according to the National Retail Association.

"Indeed, some retailers are reporting reduction rates as high as 90 per cent," NRA's David Stout said on Sunday.

Mr Stout says the ban was a "brave" move from the major supermarkets and it's paving the way for smaller businesses, who typically can't afford to risk the wrath of their customers, to follow suit.

"They're obviously (supermarkets) seen as the product stewards so a lot of people will come back to them," Mr Stout told AAP.

"Obviously the best thing for smaller businesses is to either engineer out the bag completely or have the customer pay … they should be able to consider that strategy without fear of backlash."

Both Coles and Woolworths committed to a June 30, 2018 deadline for removing single-use plastic bags last year. Picture: AAP Image/Peter RAE

Mr Stout is hopeful major retailers will continue to lead the charge towards a more sustainable industry and move to ban other single-use packaging options. "Everyone delivering things in a package need to take responsibility for what they deliver it in," he said.

"I think there's going to be a lot more pressure on all of us to be more aware of what we consume."

With NSW the only state or territory in Australia that hasn't moved to legislate to phase out plastic bags, Mr Stout says it's time to step up and quit relying on the supermarket ban to do the work.

"We're still seeing a lot of small to medium bags being used, especially in the food category, and while I get some comfort that the majors have done this voluntarily I think there still needs to be a ban in place," he said.

"For business, for the environment, for the consumer and of course even for councils which have to work to remove these things from landfills, there's a multitude of benefits on a whole to doing this."